Are we talking about the trader in the castle's lounge? I just tested him out and won 6 out of 10 games. The only idea I have is that you downloaded the game from somewhere else and it was modded there...
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Ah, the restaurant guy. There's no difference between him and Johan in the lounge except for the bet amount. I just checked his logic. So, getting several wins with a perfect 21 is either really bad luck or some changes to the game. By statistics, it's highly unlikely to happen in a prolonged time period.